Television special effects circuit for wiping video signals

Abstract

A method of wiping from one television video source to another encompasses the steps of mixing the color burst information during each horizontal blanking interval while wiping the video information carrying portion of each horizontal scan interval from one source to another. A special effects circuit for accomplishing this method includes a pair of variable gain linear amplifiers each having an input terminal coupled to a respective source of video signals to be wiped, and a circuit for providing a wipe control signal applied to the input of the amplifiers to control the gain of the amplifiers during the horizontal blanking interval in proportion to the percentage of wiping taking place, and control the variable gain amplifiers during the remaining portion of each horizontal scanning interval to apply either video from one or the other video sources. As signals from one video source are progressively wiped onto the raster, the proportionate mixing of the color burst signals progressively changes in direct proportion to the proportion of each video being displayed during the wiping process.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A special effects circuit for wiping from one composite video source to another composite video source comprising: only two variable gain linear amplifiers each having an input terminal for receiving composite video signals including color burst signals to be wiped, said amplifiers further including control input terminals and output terminals;   circuit means for providing a wipe control signal applied to the control input terminals of said variable gain amplifiers to control the gain of the amplifiers during each blanking interval in proportion to the wiping action for mixing the color burst signals from the two sources and to control the variable gain amplifiers during the remaining portion of each scanning interval in the same proportion to provide video signals to said output terminals from one or the other video sources; and   an output amplifier having an input terminal coupled to said output terminals of said variable gain amplifiers for mixing the signals from said variable gain amplifiers and including an output terminal for providing video output signals thereat.   
     
     
       2. The circuit as defined in claim 1 wherein said circuit means includes a variable direct voltage source and first gate circuit means coupled to said voltage source and including a control terminal for coupling to a source of blanking signals for providing said control signal at the output of said first gate circuit means during each blanking interval. 
     
     
       3. A special effects circuit for wiping from one composite video source to another composite video source comprising: a first variable gain linear amplifier having an input terminal for receiving video signals from a first source of composite video signals, an output terminal, and a control terminal;   a linear inverter circuit coupled to said control input terminal of said first amplifier;   a second variable gain linear amplifier having an input terminal for receiving video signals from a second source of composite video signals, an output terminal coupled to said output terminal of said first amplifier, and a control terminal;   circuit means for providing a wipe control signal applied to said control input of said second amplifier and to said inverter, said control signal having a blanking interval and a video signal interval and wherein said level of color burst voltage signals during said blanking interval is directly proportional to the proportion of video being wiped whereby the color burst signals at the output of said amplifiers during said blanking interval are proportionately mixed while the video information signals are wiped from one source to another in the same proportion.   
     
     
       4. A special effects circuit for wiping from one composite video source to another composite video source comprising: a first variable gain linear amplifier for receiving composite video signals from one source, said amplifier having an input terminal, an output terminal, and a control terminal;   a second variable gain linear amplifier for receiving composite video signals from another source, said second amplifier having an input terminal, an output terminal, and a control terminal;   a variable voltage source for providing a wiping control voltage;   an inverter coupled to said control terminal of one of said first or second amplifiers;   first and second gate circuit means having input terminals and commonly coupled output terminals, said output terminals coupled to said inverter and to the control terminal of the other of said first or second amplifiers;   means for applying blanking signals of opposite polarity to said gate circuits to enable one of said gates during a blanking interval and disable the other of said gate circuits during a blanking interval;   means coupling said variable voltage source to the input of the gate enabled during a blanking interval; and   wipe generator means coupled to said variable voltage source and including means for receiving horizontal and vertical drive signals for providing at an output terminal thereof, a wiping control signal, said output terminal of said wipe generator means coupled to said other gate circuit whereby a composite wiping control signal is provided to the commonly coupled output terminals of said gate circuits and applied to said first and second amplifiers to mix the color burst signals of the two video sources during each blanking inteval and to wipe from one video signal source to the other as the voltage from said variable source is varied in the same proportion.   
     
     
       5. The circuit as defined in claim 4 wherein said variable voltage source comprises a regulated voltage supply and a potentiometer coupled thereto to provide a selectable voltage output to control the wiping.